Hệ thống phun xăng điện tử KJetronic của Bosch

Gasoline-engine management

Gasoline Fuel-Injection
System K-Jetronic

Technical Instruction


Published by:
© Robert Bosch GmbH, 2000
Postfach 30 02 20,
D-70442 Stuttgart.
Automotive Equipment Business Sector,
Department for Automotive Services,
Technical Publications (KH/PDI2).
Editor-in-Chief:
Dipl.-Ing. (FH) Horst Bauer.
Editorial staff:
Dipl.-Ing. Karl-Heinz Dietsche,
Dipl.-Ing. (BA) Jürgen Crepin.
Presentation:
Dipl.-Ing. (FH) Ulrich Adler,
Joachim Kaiser,
Berthold Gauder, Leinfelden-Echterdingen.
Translation:
Peter Girling.
Technical graphics:
Bauer & Partner, Stuttgart.
Unless otherwise stated, the above are all
employees of Robert Bosch GmbH, Stuttgart.
Reproduction, copying, or translation of this

publication, including excerpts therefrom, is only to
ensue with our previous written consent and with
source credit.
Illustrations, descriptions, schematic diagrams,
and other data only serve for explanatory purposes
and for presentation of the text. They cannot be
used as the basis for design, installation, or scope
of delivery. We assume no liability for conformity of
the contents with national or local legal regulations.
We are exempt from liability.
We reserve the right to make changes at any time.
Printed in Germany.
Imprimé en Allemagne.
4th Edition, February 2000.
English translation of the German edition dated:
September 1998.


K-Jetronic

Since its introduction, the K-Jetronic
gasoline-injection system has proved itself in millions of vehicles.
This development was a direct result
of the advantages which are inherent
in the injection of gasoline with
regard to demands for economy of
operation, high output power, and
last but not least improvements to
the quality of the exhaust gases
emitted by the vehicle. Whereas the

call for higher engine output was the
foremost consideration at the start of
the development work on gasoline
injection, today the target is to
achieve higher fuel economy and
lower toxic emissions.
Between the years 1973 and 1995,
the highly reliable, mechanical multipoint injection system K-Jetronic
was installed as Original Equipment
in series-production vehicles. Today,
it has been superseded by gasoline
injection systems which thanks to
electronics have been vastly improved and expanded in their functions. Since this point, the K-Jetronic
has now become particularly important with regard to maintenance and
repair.
This manual will describe the
K-Jetronic’s function and its particular features.

Combustion in the gasoline engine
The spark-ignition or
Otto-cycle engine
2
Gasoline-engine management
Technical requirements
4
Cylinder charge
5
Mixture formation
7
Gasoline-injection systems

Overview
10
K-Jetronic
System overview
13
Fuel supply
14
Fuel metering
18
Adapting to operating conditions
24
Supplementary functions
30
Exhaust-gas treatment
32
Electrical circuitry
36
Workshop testing techniques
38


Combustion in
the gasoline
engine

Combustion in
the gasoline engine
The spark-ignition
or Otto-cycle engine
Operating concept

The spark-ignition or Otto-cycle1)
powerplant is an internal-combustion (IC)
engine that relies on an externallygenerated ignition spark to transform the
chemical energy contained in fuel into
kinetic energy.
Today’s standard spark-ignition engines
employ manifold injection for mixture
formation outside the combustion
chamber. The mixture formation system
produces an air/fuel mixture (based on
gasoline or a gaseous fuel), which is
then drawn into the engine by the suction
generated as the pistons descend. The
future will see increasing application of
systems that inject the fuel directly into the
combustion chamber as an alternate
concept. As the piston rises, it compresses
the mixture in preparation for the timed
ignition process, in which externallygenerated energy initiates combustion via
the spark plug. The heat released in the
Fig. 1
Reciprocating piston-engine design concept
OT = TDC (Top Dead Center); UT = BDC (Bottom
Dead Center), Vh Swept volume, VC Compressed
volume, s Piston stroke.
VC
OT
s

combustion process pressurizes the

cylinder, propelling the piston back down,
exerting force against the crankshaft and
performing work. After each combustion
stroke the spent gases are expelled from
the cylinder in preparation for ingestion of
a fresh charge of air/fuel mixture. The
primary design concept used to govern
this gas transfer in powerplants for
automotive applications is the four-stroke
principle, with two crankshaft revolutions
being required for each complete cycle.

The four-stroke principle
The four-stroke engine employs flowcontrol valves to govern gas transfer
(charge control). These valves open and
close the intake and exhaust tracts
leading to and from the cylinder:
1st stroke:
2nd stroke:
3rd stroke:
4th stroke:

Induction,
Compression and ignition,
Combustion and work,
Exhaust.

Induction stroke
Intake valve: open,
Exhaust valve: closed,

Piston travel: downward,
Combustion: none.
The piston’s downward motion increases
the cylinder’s effective volume to draw
fresh air/fuel mixture through the passage
exposed by the open intake valve.

Vh
UT

UT

2

UMM0001E

OT

Compression stroke
Intake valve: closed,
Exhaust valve: closed,
Piston travel: upward,
Combustion: initial ignition phase.
1)

After Nikolaus August Otto (1832 –1891), who
unveiled the first four-stroke gas-compression engine
at the Paris World Exhibition in 1876.

As the piston travels upward it reduces
the cylinder’s effective volume to
compress the air/fuel mixture. Just before
the piston reaches top dead center (TDC)
the spark plug ignites the concentrated
air/fuel mixture to initiate combustion.
Stroke volume Vh
and compression volume VC
provide the basis for calculating the
compression ratio
ε = (Vh+VC)/VC.
Compression ratios ε range from 7...13,
depending upon specific engine design.
Raising an IC engine’s compression ratio
increases its thermal efficiency, allowing
more efficient use of the fuel. As an
example, increasing the compression ratio
from 6:1 to 8:1 enhances thermal
efficiency by a factor of 12 %. The latitude
for increasing compression ratio is
restricted by knock. This term refers to
uncontrolled mixture inflammation characterized by radical pressure peaks.
Combustion knock leads to engine
damage. Suitable fuels and favorable
combustion-chamber configurations can
be applied to shift the knock threshold into
higher compression ranges.
Power stroke
Intake valve: closed,
Exhaust valve: closed,

Piston travel: upward,
Combustion: combustion/post-combustion phase.

The ignition spark at the spark plug
ignites the compressed air/fuel mixture,
thus initiating combustion and the
attendant temperature rise.
This raises pressure levels within the
cylinder to propel the piston downward.
The piston, in turn, exerts force against
the crankshaft to perform work; this
process is the source of the engine’s
power.
Power rises as a function of engine speed
and torque (P = M⋅ω).
A transmission incorporating various
conversion ratios is required to adapt the
combustion engine’s power and torque
curves to the demands of automotive
operation under real-world conditions.

Otto cycle

Exhaust stroke
Intake valve: closed,
Exhaust valve: open,
Piston travel: upward,
Combustion: none.
As the piston travels upward it forces the
spent gases (exhaust) out through the

passage exposed by the open exhaust
valve. The entire cycle then recommences
with a new intake stroke. The intake and
exhaust valves are open simultaneously
during part of the cycle. This overlap
exploits gas-flow and resonance patterns
to promote cylinder charging and
scavenging.

Fig. 2
Operating cycle of the 4-stroke spark-ignition engine
Stroke 2: Compression

Stroke 3: Combustion

Stroke 4: Exhaust

UMM0011E

Stroke 1: Induction

3


Gasolineengine
management

Gasolineengine management
Technical requirements
Spark-ignition (SI)

engine torque
The power P furnished by the sparkignition engine is determined by the
available net flywheel torque and the
engine speed.
The net flywheel torque consists of the
force generated in the combustion
process minus frictional losses (internal
friction within the engine), the gasexchange losses and the torque required
to drive the engine ancillaries (Figure 1).
The combustion force is generated
during the power stroke and is defined by
the following factors:
– The mass of the air available for
combustion once the intake valves
have closed,
– The mass of the simultaneously
available fuel, and
– The point at which the ignition spark
initiates combustion of the air/fuel
mixture.

Primary enginemanagement functions
The engine-management system’s first
and foremost task is to regulate the
engine’s torque generation by controlling
all of those functions and factors in the
various engine-management subsystems
that determine how much torque is
generated.
Cylinder-charge control

In Bosch engine-management systems
featuring electronic throttle control (ETC),
the “cylinder-charge control” subsystem
determines the required induction-air
mass and adjusts the throttle-valve
opening accordingly. The driver exercises
direct control over throttle-valve opening
on conventional injection systems via the
physical link with the accelerator pedal.
Mixture formation
The “mixture formation” subsystem calculates the instantaneous mass fuel
requirement as the basis for determining
the correct injection duration and optimal
injection timing.

Fig. 1
Driveline torque factors
1

Air mass (fresh induction charge)
Fuel mass

Engine

1

Combustion
output torque

Ignition angle (firing point)

Gas-transfer and friction
Ancillaries
Clutch/converter losses and conversion ratios
Transmission losses and conversion ratios

4

2

3

4

Flywheel
Engine
output torque torque
–
–

Clutch
–
–

Drive
Trans- force
mission
–
–

UMM0545-1E

1 Ancillary equipment
(alternator,
a/c compressor, etc.),
2 Engine,
3 Clutch,
4 Transmission.


emissions control system (Figure 2). The
air entering through the throttle-valve and
remaining in the cylinder after intakevalve closure is the decisive factor
defining the amount of work transferred
through the piston during combustion,
and thus the prime determinant for the
amount of torque generated by the
engine. In consequence, modifications to
enhance maximum engine power and
torque almost always entail increasing
the maximum possible cylinder charge.
The theoretical maximum charge is
defined by the volumetric capacity.

Ignition
Finally, the “ignition” subsystem determines the crankshaft angle that
corresponds to precisely the ideal instant
for the spark to ignite the mixture.
The purpose of this closed-loop control
system is to provide the torque
demanded by the driver while at the

same time satisfying strict criteria in the
areas of
– Exhaust emissions,
– Fuel consumption,
– Power,
– Comfort and convenience, and
– Safety.

Cylinder
charge

Residual gases
The portion of the charge consisting of
residual gases is composed of
– The exhaust-gas mass that is not
discharged while the exhaust valve is
open and thus remains in the cylinder,
and
– The mass of recirculated exhaust gas
(on systems with exhaust-gas recirculation, Figure 2).
The proportion of residual gas is determined by the gas-exchange process.
Although the residual gas does not
participate directly in combustion, it does
influence ignition patterns and the actual
combustion sequence. The effects of this
residual-gas component may be thoroughly
desirable under part-throttle operation.
Larger throttle-valve openings to compensate for reductions in fresh-gas filling

Cylinder charge

Elements
The gas mixture found in the cylinder
once the intake valve closes is referred to
as the cylinder charge, and consists of
the inducted fresh air-fuel mixture along
with residual gases.
Fresh gas
The fresh mixture drawn into the cylinder
is a combination of fresh air and the fuel
entrained with it. While most of the fresh
air enters through the throttle valve,
supplementary fresh gas can also be
drawn in through the evaporativeFig. 2
Cylinder charge in the spark-ignition engine

2

3

1
α

4

5
11

6

12

7

10
8
9
UMM0544-1Y

1 Air and fuel vapor,
2 Purge valve
with variable aperture,
3 Link to evaporative-emissions
control system,
4 Exhaust gas,
5 EGR valve with
variable aperture,
6 Mass airflow (barometric pressure pU),
7 Mass airflow
(intake-manifold pressure ps),
8 Fresh air charge
(combustion-chamber pressure pB),
9 Residual gas charge
(combustion-chamber pressure pB),
10 Exhaust gas (back-pressure pA),
11 Intake valve,
12 Exhaust valve,
α Throttle-valve angle.

5

Control elements
Throttle valve
The power produced by the sparkignition engine is directly proportional to
the mass airflow entering it. Control of
engine output and the corresponding
torque at each engine speed is regulated
by governing the amount of air being
inducted via the throttle valve. Leaving
the throttle valve partially closed restricts
the amount of air being drawn into the
engine and reduces torque generation.
The extent of this throttling effect
depends on the throttle valve’s position
and the size of the resulting aperture.
The engine produces maximum power
when the throttle valve is fully open
(WOT, or wide open throttle).
Figure 3 illustrates the conceptual
correlation between fresh-air charge
density and engine speed as a function
of throttle-valve aperture.

6

Gas exchange
The intake and exhaust valves open and
close at specific points to control the
transfer of fresh and residual gases. The
ramps on the camshaft lobes determine

both the points and the rates at which the
valves open and close (valve timing) to
define the gas-exchange process, and
with it the amount of fresh gas available
for combustion.
Valve overlap defines the phase in which
the intake and exhaust valves are open
simultaneously, and is the prime factor in
determining the amount of residual gas
remaining in the cylinder. This process is
known
as
"internal"
exhaust-gas
recirculation. The mass of residual gas
can also be increased using "external"
exhaust-gas recirculation, which relies

on a supplementary EGR valve linking
the intake and exhaust manifolds. The
engine ingests a mixture of fresh air and
exhaust gas when this valve is open.
Pressure charging
Because maximum possible torque is
proportional to fresh-air charge density, it
is possible to raise power output by
compressing the air before it enters the
cylinder.
Dynamic pressure charging
A supercharging (or boost) effect can be

obtained by exploiting dynamics within
the intake manifold. The actual degree of
boost will depend upon the manifold’s
configuration as well as the engine’s
instantaneous
operating
point
(essentially a function of the engine’s
speed, but also affected by load factor).
The option of varying intake-manifold
geometry while the vehicle is actually
being driven, makes it possible to employ
dynamic precharging to increase the
maximum available charge mass through
a wide operational range.
Mechanical supercharging
Further increases in air mass are
available through the agency of
Fig. 3
Throttle-valve map for spark-ignition engine
Throttle valve at intermediate aperture

Throttle valve
completely open

Throttle valve
completely closed
min.
Idle

max.
RPM

UMM0543-1E

are needed to meet higher torque
demand. These higher angles reduce the
engine’s pumping losses, leading to
lower fuel consumption. Precisely regulated injection of residual gases can
also modify the combustion process to
reduce emissions of nitrous oxides (NOx)
and unburned hydrocarbons (HC).

Fresh gas charge

Gasolineengine
management


mechanically driven compressors powered by the engine’s crankshaft, with the
two elements usually rotating at an invariable relative ratio. Clutches are often
used to control compressor activation.

Mixture formation

Exhaust-gas turbochargers
Here the energy employed to power the
compressor is extracted from the exhaust
gas. This process uses the energy that
naturally-aspirated

engines
cannot
exploit directly owing to the inherent
restrictions imposed by the gas expansion characteristics resulting from the
crankshaft concept. One disadvantage is
the higher back-pressure in the exhaust
gas exiting the engine. This backpressure stems from the force needed to
maintain compressor output.
The exhaust turbine converts the
exhaust-gas energy into mechanical
energy, making it possible to employ an
impeller to precompress the incoming
fresh air. The turbocharger is thus a
combination of the turbine in the exhaustfas flow and the impeller that compresses
the intake air.
Figure 4 illustrates the differences in the
torque curves of a naturally-aspirated
engine and a turbocharged engine.

Air-fuel mixture
Operation of the spark-ignition engine is
contingent upon availability of a mixture
with a specific air/fuel (A/F) ratio. The
theoretical ideal for complete combustion
is a mass ratio of 14.7:1, referred to as
the stoichiometric ratio. In concrete terms
this translates into a mass relationship of
14.7 kg of air to burn 1 kg of fuel, while
the corresponding volumetric ratio is
roughly 9,500 litres of air for complete

combustion of 1 litre of fuel.

Fig. 4
Torque curves for turbocharged
and atmospheric-induction engines
with equal power outputs
1 Engine with turbocharger,
2 Atmospheric-induction engine.

Engine torque Md

1

2

Engine rpm nn

3

4

1

1

UMM0459-1E

2

4

Parameters

The air-fuel mixture is a major factor in
determining the spark-ignition engine’s
rate of specific fuel consumption.
Genuine complete combustion and
absolutely minimal fuel consumption
would be possible only with excess air,
but here limits are imposed by such
considerations as mixture flammability
and the time available for combustion.
The air-fuel mixture is also vital in
determining the efficiency of exhaust-gas
treatment system. The current state-ofthe-art features a 3-way catalytic
converter, a device which relies on a
stoichiometric A/F ratio to operate at
maximum efficiency and reduce undesirable exhaust-gas components by
more than 98 %.
Current engines therefore operate with a
stoichiometric A/F ratio as soon as the
engine’s operating status permits

1

1

Mixture
formation

Certain engine operating conditions
make mixture adjustments to nonstoichiometric ratios essential. With a
cold engine for instance, where specific
adjustments to the A/F ratio are required.
As this implies, the mixture-formation
system must be capable of responding to
a range of variable requirements.

7


Gasolineengine
management

Excess-air factor
The designation l (lambda) has been
selected to identify the excess-air factor
(or air ratio) used to quantify the spread
between the actual current mass A/F ratio
and the theoretical optimum (14.7:1):
λ = Ratio of induction air mass to air
requirement for stoichiometric combustion.
λ = 1: The inducted air mass corresponds
to the theoretical requirement.
λ < 1: Indicates an air deficiency,
producing a corresponding rich mixture.
Maximum power is derived from λ =
0.85...0.95.
λ > 1: This range is characterized by
excess air and lean mixture, leading to

lower fuel consumption and reduced
power. The potential maximum value for λ
– called the “lean-burn limit (LML)” – is
essentially defined by the design of the
engine and of its mixture formation/induction system. Beyond the
lean-burn limit the mixture ceases to be
ignitable and combustion miss sets in,
accompanied by substantial degeneration of operating smoothness.
In engines featuring systems to inject fuel
directly into the chamber, these operate
with substantially higher excess-air
factors (extending to λ = 4) since combustion proceeds according to different
laws.
Spark-ignition engines with manifold
injection produce maximum power at air

deficiencies of 5...15 % (λ = 0.95...0.85),
but maximum fuel economy comes in at
10...20 % excess air (λ = 1.1...1.2).
Figures 1 and 2 illustrate the effect of the
excess-air factor on power, specific fuel
consumption and generation of toxic
emissions. As can be seen, there is no
single excess-air factor which can
simultaneously generate the most
favorable levels for all three factors. Air
factors of λ = 0.9...1.1 produce
“conditionally optimal” fuel economy with
“conditionally optimal” power generation
in actual practice.

Once the engine warms to its normal
operating temperature, precise and
consistent maintenance of λ = 1 is vital
for the 3-way catalytic treatment of
exhaust gases. Satisfying this requirement entails exact monitoring of
induction-air mass and precise metering
of fuel mass.
Optimal combustion from current engines equipped with manifold injection
relies on formation of a homogenous
mixture as well as precise metering of the
injected fuel quantity. This makes
effective atomization essential. Failure to
satisfy this requirement will foster the
formation of large droplets of condensed
fuel on the walls of the intake tract and in
the combustion chamber. These droplets
will fail to combust completely and the
ultimate result will be higher HC
emissions.

Fig. 1

Fig. 2

Effects of excess-air factor λ on power P and
specific fuel consumption be.

Effect of excess-air factor λ on untreated
exhaust emissions

a Rich mixture (air deficiency),
b Lean mixture (excess air).
HC

NOX

Power P ,
Specific fuel consumption be

CO

0.8

8

b

1.0
1.2
Excess-air factor λ

UMK0033E

a

0.6

0.8

1.0

1.2
Excess-air factor λ

1.4

UMK0032E

be

Relative quantities of
CO; HC; NOX

P


Adapting to specific
operating conditions
Certain operating states cause fuel
requirements to deviate substantially from
the steady-state requirements of an engine
warmed to its normal temperature, thus
necessitating corrective adaptations in the
mixture-formation apparatus. The following descriptions apply to the conditions
found in engines with manifold injection.
Cold starting
During cold starts the relative quantity of
fuel in the inducted mixture decreases: the
mixture “goes lean.” This lean-mixture
phenomenon stems from inadequate
blending of air and fuel, low rates of fuel

vaporization, and condensation on the
walls of the inlet tract, all of which are
promoted by low temperatures. To compensate for these negative factors, and to
facilitate cold starting, supplementary fuel
must be injected into the engine.
Post-start phase
Following
low-temperature
starts,
supplementary fuel is required for a brief
period, until the combustion chamber
heats up and improves the internal
mixture formation. This richer mixture
also increases torque to furnish a
smoother transition to the desired idle
speed.
Warm-up phase
The warm-up phase follows on the heels
of the starting and immediate post-start
phases. At this point the engine still
requires an enriched mixture to offset the
fuel condensation on the intake-manifold
walls. Lower temperatures are synonymous with less efficient fuel processing (owing to factors such as poor mixing of air and fuel and reduced fuel vaporization). This promotes fuel precipitation within the intake manifold, with
the formation of condensate fuel that will
only vaporize later, once temperatures
have increased. These factors make it
necessary to provide progressive mixture
enrichment in response to decreasing
temperatures.

Idle and part-load
Idle is defined as the operating status in
which the torque generated by the engine
is just sufficient to compensate for friction
losses. The engine does not provide
power to the flywheel at idle. Part-load (or
part-throttle) operation refers to the
range of running conditions between idle
and generation of maximum possible
torque. Today’s standard concepts rely
exclusively on stoichiometric mixtures for
the operation of engines running at idle
and part-throttle once they have warmed
to their normal operating temperatures.

Mixture
formation

Full load (WOT)
At WOT (wide-open throttle) supplementary enrichment may be required. As
Figure 1 indicates, this enrichment
furnishes maximum torque and/or power.
Acceleration and deceleration
The fuel’s vaporization potential is strongly
affected by pressure levels inside the
intake manifold. Sudden variations in
manifold pressure of the kind encountered
in response to rapid changes in throttlevalve aperture cause fluctuations in the
fuel layer on the walls of the intake tract.
Spirited acceleration leads to higher

manifold pressures. The fuel responds
with lower vaporization rates and the fuel
layer within the manifold runners expands.
A portion of the injected fuel is thus lost in
wall condensation, and the engine goes
lean for a brief period, until the fuel layer
restabilizes. In an analogous, but inverted,
response pattern, sudden deceleration
leads to rich mixtures. A temperaturesensitive correction function (transition
compensation) adapts the mixture to
maintain optimal operational response
and ensure that the engine receives the
consistent air/fuel mixture needed for
efficient catalytic-converter performance.
Trailing throttle (overrun)
Fuel metering is interrupted during trailing
throttle. Although this expedient saves
fuel on downhill stretches, its primary
purpose is to guard the catalytic converter
against overheating stemming from poor
and incomplete combustion (misfiring).

9


Gasolineinjection
systems

Gasoline-injection systems

Carburetors and gasoline-injection systems are designed for a single purpose:
To supply the engine with the optimal airfuel mixture for any given operating
conditions. Gasoline injection systems,
and electronic systems in particular, are
better at maintaining air-fuel mixtures
within precisely defined limits, which
translates into superior performance in
the areas of fuel economy, comfort and
convenience, and power. Increasingly
stringent mandates governing exhaust
emissions have led to a total eclipse of the
carburetor in favor of fuel injection.
Although current systems rely almost
exclusively on mixture formation outside
the combustion chamber, concepts based
on internal mixture formation – with fuel
being injected directly into the combustion
chamber – were actually the foundation
for the first gasoline-injection systems. As
these systems are superb instruments for
achieving further reductions in fuel
consumption, they are now becoming an
increasingly significant factor.

Representative examples are the various
versions of the KE and L-Jetronic systems
(Figure 1).
Mechanical injection systems
The K-Jetronic system operates by
injecting continually, without an external drive being necessary. Instead of

being determined by the injection valve,
fuel mass is regulated by the fuel
distributor.
Combined mechanical-electronic
fuel injection
Although the K-Jetronic layout served as
the mechanical basis for the KE-Jetronic
system, the latter employs expanded
data-monitoring functions for more
precise adaptation of injected fuel
quantity to specific engine operating
conditions.
Electronic injection systems
Injection systems featuring electronic
control rely on solenoid-operated injection
Fig. 1

Overview
Systems with
external mixture formation
The salient characteristic of this type of
system is the fact that it forms the air-fuel
mixture outside the combustion chamber,
inside the intake manifold.

Multipoint fuel injection (MPI)
1 Fuel,
2 Air,
3 Throttle valve,
4 Intake manifold,

5 Injectors,
6 Engine.
4

2
3

1

10

6

UMK0662-2Y

5

Multipoint fuel injection
Multipoint fuel injection forms the ideal
basis for complying with the mixtureformation criteria described above. In this
type of system each cylinder has its own
injector discharging fuel into the area
directly in front of the intake valve.


valves for intermittent fuel discharge. The
actual injected fuel quantity is regulated
by controlling the injector's opening time
(with the pressure-loss gradient through
the valve being taken into account in

calculations as a known quantity).
Examples: L-Jetronic, LH-Jetronic, and
Motronic as an integrated engine-management system.
Single-point fuel injection
Single-point (throttle-body injection (TBI))
fuel injection is the concept behind this
electronically-controlled injection system
in which a centrally located solenoidoperated injection valve mounted
upstream from the throttle valve sprays
fuel intermittently into the manifold. MonoJetronic and Mono-Motronic are the
Bosch systems in this category (Figure 2).

Systems for internal
mixture formation
Direct-injection (DI) systems rely on
solenoid-operated injection valves to spray
fuel directly into the combustion chamber;
the actual mixture-formation process takes
place within the cylinders, each of which
has its own injector (Figure 3). Perfect
atomization of the fuel emerging from the
injectors is vital for efficient combustion.
Under normal operating conditions, DI
engines draw in only air instead of the
Fig. 2

combination of air and fuel common to
conventional injection systems. This is one
of the new system's prime advantages: It
banishes all potential for fuel condensation

within the runners of the intake manifold.
External mixture formation usually
provides a homogenous, stoichiometric airfuel mixture throughout the entire
combustion chamber. In contrast, shifting
the mixture-preparation process into the
combustion chamber provides for two
distinctive operating modes:
With stratified-charge operation, only the
mixture directly adjacent to the spark plug
needs to be ignitable. The remainder of the
air-fuel charge in the combustion chamber
can consist solely of fresh and residual
gases, without unburned fuel. This strategy
furnishes an extremely lean overall mixture
for idling and part-throttle operation, with
commensurate
reductions
in
fuel
consumption.
Homogenous operation reflects the
conditions encountered in external mixture
formation
by
employing
uniform
consistency for the entire air-fuel charge
throughout the combustion chamber.
Under these conditions all of the fresh air
within the chamber participates in the

combustion process. This operational
mode is employed for WOT operation.
MED-Motronic is used for closed-loop
control of DI gasoline engines.

Overview

Fig. 3

Throttle-body fuel injection (TBI)

Direct fuel injection (DI)

1 Fuel,
2 Air,
3 Throttle valve,
4 Intake manifold,
5 Injector,
6 Engine.
4

1 Fuel,
2 Air,
3 Throttle valve
(ETC),
4 Intake manifold,
5 Injectors,
6 Engine.
4

2
3

2
3

1
1

UMK0663-2Y

6

6

UMK1687-2Y

5

5

11


The story of
fuel injection

The story of fuel injection
The story of fuel injection extends
back to cover a period of almost one

hundred years.
The Gasmotorenfabik Deutz was
manufacturing plunger pumps for injecting fuel in a limited production
series as early as 1898.
A short time later the uses of the venturi-effect for carburetor design were
discovered, and fuel-injection systems
based on the technology of the time
ceased to be competitive.
Bosch started research on gasolineinjection pumps in 1912. The first
aircraft engine featuring Bosch fuel injection, a 1,200-hp unit, entered series
production in 1937; problems with carburetor icing and fire hazards had lent
special impetus to fuel-injection development work for the aeronautics field.
This development marks the beginning of the era of fuel injection at
Bosch, but there was still a long path
to travel on the way to fuel injection for
passenger cars.
1951 saw a Bosch direct-injection unit
being featured as standard equipment
on a small car for the first time. Several years later a unit was installed in
the 300 SL, the legendary production
sports car from Daimler-Benz.
In the years that followed, development on mechanical injection pumps
continued, and ...
In 1967 fuel injection took another
giant step forward: The first electronic
Bosch gasoline fuel injection
from the year 1954

12

injection system: the intake-pressurecontrolled D-Jetronic!
In 1973 the air-flow-controlled L-Jetronic appeared on the market, at the
same time as the K-Jetronic, which featured mechanical-hydraulic control and
was also an air-flow-controlled system.
In 1976, the K-Jetronic was the first
automotive system to incorporate a
Lambda closed-loop control.
1979 marked the introduction of a new
system: Motronic, featuring digital processing for numerous engine functions. This system combined L-Jetronic with electronic program-map control for the ignition. The first automotive microprocessor!
In 1982, the K-Jetronic model became
available in an expanded configuration, the KE-Jetronic, including an
electronic closed-loop control circuit
and a Lambda oxygen sensor.
These were joined by Bosch MonoJetronic in 1987: This particularly costefficient single-point injection unit
made it feasible to equip small vehicles
with Jetronic, and once and for all made
the carburetor absolutely superfluous.
By the end of 1997, around 64 million
Bosch engine-management systems
had been installed in countless types of
vehicles since the introduction of the
D-Jetronic in 1967. In 1997 alone, the
figure was 4.2 million, comprised of
1 million throttle-body injection (TBI)
systems and 3.2 million multipoint fuelinjection (MPI) systems.


K-Jetronic
System overview
The K-Jetronic is a mechanically and

hydraulically controlled fuel-injection system which needs no form of drive and
which meters the fuel as a function of the
intake air quantity and injects it continuously onto the engine intake valves.
Specific operating conditions of the
engine require corrective intervention in
mixture formation and this is carried out
by the K-Jetronic in order to optimize
starting and driving performance, power
output and exhaust composition. Owing
to the direct air-flow sensing, the K-Jetronic system also allows for engine
variations and permits the use of facilities
for exhaust-gas aftertreatment for which
precise metering of the intake air quantity
is a prerequisite.
The K-Jetronic was originally designed
as a purely mechanical injection system.
Today, using auxiliary electronic equipment, the system also permits the use of
lambda closed-loop control.
The K-Jetronic fuel-injection system
covers the following functional areas:
– Fuel supply,
– Air-flow measurement and
– Fuel metering.

Fuel supply
An electrically driven fuel pump delivers
the fuel to the fuel distributor via a fuel
accumulator and a filter. The fuel distributor allocates this fuel to the injection
valves of the individual cylinders.

K-Jetronic

Air-flow measurement
The amount of air drawn in by the engine
is controlled by a throttle valve and
measured by an air-flow sensor.
Fuel metering
The amount of air, corresponding to the
position of the throttle plate, drawn in by
the engine serves as the criterion for
metering of the fuel to the individual
cylinders. The amount of air drawn in by
the engine is measured by the air-flow
sensor which, in turn, controls the fuel
distributor. The air-flow sensor and the
fuel distributor are assemblies which
form part of the mixture control unit.
Injection occurs continuously, i.e. without
regard to the position of the intake valve.
During the intake-valve closed phase, the
fuel is “stored”. Mixture enrichment is
controlled in order to adapt to various
operating conditions such as start, warmup, idle and full load. In addition, supplementary functions such as overrun fuel
cutoff, engine-speed limiting and closedloop lambda control are possible.

Fig. 1
Functional schematic of the K-Jetronic

Electric
fuel pump

Air filter
Air

Fuel
accumulator

Air-flow
sensor

Mixture
control unit

Fuel filter

Fuel
distributor

Injection valves

Throttle valve
Mixture
Intake ports

Combustion
chamber

UMK0009E

Fuel

13


Gasolineinjection
systems

Fuel supply
The fuel supply system comprises
– Electric fuel pump,
– Fuel accumulator,
– Fine filter,
– Primary-pressure regulator and
– Injection valves.
An electrically driven roller-cell pump
pumps the fuel from the fuel tank at a
pressure of over 5 bar to a fuel accumulator and through a filter to the fuel
distributor. From the fuel distributor the
fuel flows to the injection valves. The
injection valves inject the fuel continuously into the intake ports of the
engine. Thus the system designation K
(taken from the German for continuous).
When the intake valves open, the mixture
is drawn into the cylinder.
The fuel primary-pressure regulator
maintains the supply pressure in the
system constant and reroutes the excess
fuel back to the fuel tank.
Owing to continual scavenging of the fuel
supply system, there is always cool fuel

available. This avoids the formation of
fuel-vapor bubbles and achieves good
hot starting behavior.
Electric fuel pump
The electric fuel pump is a roller-cell
pump driven by a permanent-magnet
electric motor.
The rotor plate which is eccentrically
mounted in the pump housing is fitted
with metal rollers in notches around its
circumference which are pressed against
the pump housing by centrifugal force
and act as rolling seals. The fuel is carried in the cavities which form between
the rollers. The pumping action takes
place when the rollers, after having
closed the inlet bore, force the trapped
fuel in front of them until it can escape
from the pump through the outlet bore
(Figure 4). The fuel flows directly around
the electric motor. There is no danger of
explosion, however, because there is
never an ignitable mixture in the pump
housing.

Fig. 2
Schematic diagram of the K-Jetronic system with closed-loop lambda control
1 Fuel tank, 2 Electric fuel pump, 3 Fuel accumulator, 4 Fuel filter, 5 Warm-up regulator, 6 Injection valve,
7 Intake manifold, 8 Cold-start valve, 9 Fuel distributor, 10 Air-flow sensor, 11 Timing valve, 12 Lambda
sensor, 13 Thermo-time switch, 14 Ignition distributor, 15 Auxiliary-air device, 16 Throttle-valve switch,

17 ECU, 18 Ignition and starting switch, 19 Battery.

1

3
5
2

4

11

8

9

7

12

13

14

10
15

16

17

18

14

19

BOSCH
UMK0077Y

6


1 Suction side, 2 Pressure limiter, 3 Roller-cell
pump, 4 Motor armature, 5 Check valve,
6 Pressure side.
2 3

4

5

6
UMK0121-2Y

1

Fig. 3

Fig. 4
Operation of roller-cell pump

1 Suction side, 2 Rotor plate, 3 Roller,
4 Roller race plate, 5 Pressure side.
2 3

4

1

5
UMK0120-2Y

Fuel accumulator
The fuel accumulator maintains the
pressure in the fuel system for a certain
time after the engine has been switched
off in order to facilitate restarting, particularly when the engine is hot. The special design of the accumulator housing
(Figure 5) deadens the sound of the fuel
pump when the engine is running.
The interior of the fuel accumulator is
divided into two chambers by means of a
diaphragm. One chamber serves as the
accumulator for the fuel whilst the other
represents the compensation volume
and is connected to the atmosphere or to
the fuel tank by means of a vent fitting.
During operation, the accumulator
chamber is filled with fuel and the diaphragm is caused to bend back against
the force of the spring until it is halted by
the stops in the spring chamber. The
diaphragm remains in this position, which

corresponds to the maximum accumulator volume, as long as the engine is
running.

K-Jetronic

Electric fuel pump

Fig. 5
Fuel accumulator
a Empty, b Full.
1 Spring chamber, 2 Spring, 3 Stop, 4 Diaphragm,
5 Accumulator volume, 6 Fuel inlet or outlet,
7 Connection to the atmosphere.
a

7

1

2

3 4

5

6

b

UMK1653Y

The electric fuel pump delivers more fuel
than the maximum requirement of the
engine so that compression in the fuel
system can be maintained under all operating conditions. A check valve in the
pump decouples the fuel system from
the fuel tank by preventing reverse flow of
fuel to the fuel tank.
The electric fuel pump starts to operate
immediately when the ignition and starting switches are operated and remains
switched on continuously after the engine
has started. A safety circuit is incorporated to stop the pump running and, thus,
to prevent fuel being delivered if the ignition is switched on but the engine has
stopped turning (for instance in the case
of an accident).
The fuel pump is located in the immediate vicinity of the fuel tank and requires
no maintenance.

15


Fuel filter
The fuel filter retains particles of dirt
which are present in the fuel and which
would otherwise have an adverse effect
on the functioning of the injection system.
The fuel filter contains a paper element
with a mean pore size of 10 µm backed
up by a fluff trap. This combination
ensures a high degree of cleaning.

The filter is held in place in the housing
by means of a support plate. It is fitted in
the fuel line downstream from the fuel
accumulator and its service life depends
upon the amount of dirt in the fuel. It is
imperative that the arrow on the filter
housing showing the direction of fuel flow
through the filter is observed when the
filter is replaced.

Fuel filter
1 Paper element,
2 Strainer,
1
3 Support
plate.

2

3

UMK0119Y

Gasolineinjection
systems

Fig. 6

delivery drops slightly, the plunger is
shifted by the spring to a corresponding

new position and in doing so closes off
the port slightly through which the excess
fuel returns to the tank. This means that
less fuel is diverted off at this point and
the system pressure is controlled to its
specified level.
When the engine is switched off, the fuel
pump also switches off and the primary
pressure drops below the opening pressure of the injection valves. The pressure
regulator then closes the return-flow port
and thus prevents the pressure in the fuel
system from sinking any further (Fig. 8).

Primary-pressure regulator
The primary-pressure regulator maintains the pressure in the fuel system
constant.
It is incorporated in the fuel distributor
and holds the delivery pressure (system
pressure) at about 5 bar. The fuel pump
always delivers more fuel than is required
by the vehicle engine, and this causes a
plunger to shift in the pressure regulator
and open a port through which excess
fuel can return to the tank.
The pressure in the fuel system and the
force exerted by the spring on the
pressure-regulator plunger balance each
other out. If, for instance, fuel-pump

Fuel-injection valves

The injection valves open at a given pressure and atomize the fuel through oscillation of the valve needle. The injection
valves inject the fuel metered to them into
the intake passages and onto the intake
valves. They are secured in special

Fig. 7
Primary-pressure regulator fitted to fuel distributor
a In rest position, b In actuated position.
1 System-pressure entry, 2 Seal, 3 Return to fuel tank, 4 Plunger, 5 Spring.

a

b

2

16

3

4

5

UMK1495Y

1


K-Jetronic

Pressure curve after engine switchoff
Firstly pressure falls from the normal system
pressure (1) to the pressure-regulator closing
pressure (2). The fuel accumulator then causes
it to increase to the level (3) which is below the
opening pressure (4) of the injection valves.
bar

1

4
3

Pressure p

2

Time t

ms

UMK0018E

holders to insulate them against the heat
radiated from the engine. The injection
valves have no metering function themselves, and open of their own accord
when the opening pressure of e.g. 3.5
bar is exceeded. They are fitted with a
valve needle (Fig. 9) which oscillates

(“chatters”) audibly at high frequency
when fuel is injected. This results in excellent atomization of the fuel even with
the smallest of injection quantities. When
the engine is switched off, the injection
valves close tightly when the pressure in
the fuel-supply system drops below their
opening pressure. This means that no
more fuel can enter the intake passages
once the engine has stopped.

Fig. 8

Fig. 9
Fuel-injection valve
a In rest position,
b In actuated position.
1 Valve housing,
2 Filter,
3 Valve needle,
4 Valve seat.

UMK0042Y

b

3
4

UMK0069-2Y

2

a
Fig. 10
Spray pattern of an injection valve without
air-shrouding (left) and with air-shrouding (right).

1

UMK0041Y

Air-shrouded fuel-injection valves
Air-shrouded injection valves improve the
mixture formation particularly at idle.
Using the pressure drop across the
throttle valve, a portion of the air inducted
by the engine is drawn into the cylinder
through the injection valve (Fig. 20): The
result is excellent atomization of the fuel
at the point of exit (Fig. 10). Air-shrouded
injection valves reduce fuel consumption
and toxic emission constituents.

17


Gasolineinjection
systems

Fuel metering

Principle of the air-flow sensor

The task of the fuel-management system
is to meter a quantity of fuel corresponding to the intake air quantity.
Basically, fuel metering is carried out
by the mixture control unit. This comprises the air-flow sensor and the fuel
distributor.
In a number of operating modes however,
the amount of fuel required deviates
greatly from the “standard” quantity and it
becomes necessary to intervene in the
mixture formation system (see section
“Adaptation to operating conditions”).

a Small amount of air drawn in: sensor plate only
lifted slightly, b Large amount of air drawn in:
sensor plate is lifted considerably further.

a

h

b

Air-flow sensor
The quantity of air drawn in by the engine
is a precise measure of its operating
load. The air-flow sensor operates according to the suspended-body principle,
and measures the amount of air drawn in

by the engine.
The intake air quantity serves as the
main actuating variable for determining
the basic injection quantity. It is the
appropriate physical quantity for deriving
the fuel requirement, and changes in the
induction characteristics of the engine
have no effect upon the formation of the

UMK0072Y

h

Fig. 11

air-fuel mixture. Since the air drawn in by
the engine must pass through the air-flow
sensor before it reaches the engine, this
means that it has been measured and
the control signal generated before it
actually enters the engine cylinders. The
result is that, in addition to other
measures described below, the correct
mixture adaptation takes place at all
times.

Fig. 12
Updraft
air-flow sensor
a Sensor plate in its

zero position,
b Sensor plate in its
operating position.

1

2

3

4

5

a

1 Air funnel,
2 Sensor plate,
3 Relief cross-section,
4 Idle-mixture
adjusting screw,
5 Pivot,
6 Lever,
7 Leaf spring.

7

6

18

UMK1654Y

b


K-Jetronic

Barrel with metering slits
1 Intake air, 2 Control pressure, 3 Fuel inlet,
4 Metered quantity of fuel, 5 Control plunger,
6 Barrel with metering slits, 7 Fuel distributor.
7
2
5
4

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6
4

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3

1

UMK1496Y

The air-flow sensor is located upstream
of the throttle valve so that it measures all
the air which enters the engine cylinders.
It comprises an air funnel in which the

sensor plate (suspended body) is free to
pivot. The air flowing through the funnel
deflects the sensor plate by a given
amount out of its zero position, and this
movement is transmitted by a lever system to a control plunger which determines the basic injection quantity required for the basic functions. Considerable pressure shocks can occur in the
intake system if backfiring takes place in
the intake manifold. For this reason, the
air-flow sensor is so designed that the
sensor plate can swing back in the
opposite direction in the event of misfire,
and past its zero position to open a relief
cross-section in the funnel. A rubber
buffer limits the downward stroke (the
upwards stroke on the downdraft air-flow
sensor). A counterweight compensates
for the weight of the sensor plate and
lever system (this is carried out by an
extension spring on the downdraft airflow sensor). A leaf spring ensures the
correct zero position in the switched-off
phase.

Fig. 13

Fuel distributor
Depending upon the position of the plate
in the air-flow sensor, the fuel distributor
meters the basic injection quantity to the
individual engine cylinders. The position
of the sensor plate is a measure of the
amount of air drawn in by the engine. The

position of the plate is transmitted to the
control plunger by a lever.

Fig. 14
Barrel with metering slits and control plunger
a Zero (inoperated position), b Part load, c Full load.
1 Control pressure, 2 Control plunger, 3 Metering slit in the barrel, 4 Control edge, 5 Fuel inlet,
6 Barrel with metering slits.

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1

2
3
4

5
6

b

,,,,,,
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c

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UMK1497Y

a

19


20

Depending upon its position in the barrel
with metering slits, the control plunger
opens or closes the slits to a greater or
lesser extent. The fuel flows through the
open section of the slits to the differential
pressure valves and then to the fuel
injection valves. If sensor-plate travel is
only small, then the control plunger is
lifted only slightly and, as a result, only a
small section of the slit is opened for the
passage of fuel. With larger plunger
travel, the plunger opens a larger section
of the slits and more fuel can flow. There
is a linear relationship between sensorplate travel and the slit section in the
barrel which is opened for fuel flow.
A hydraulic force generated by the socalled control pressure is applied to the
control plunger. It opposes the movement
resulting from sensor-plate deflection.
One of its functions is to ensure that the
control plunger follows the sensor-plate
movement immediately and does not, for
instance, stick in the upper end position
when the sensor plate moves down again.
Further functions of the control pressure
are discussed in the sections “Warm-up
enrichment” and “Full-load enrichment”.
Control pressure
The control pressure is tapped from the
primary pressure through a restriction
bore (Figure 16). This restriction bore

serves to decouple the control-pressure
circuit and the primary-pressure circuit
from one another. A connection line joins
the fuel distributor and the warm-up
regulator (control-pressure regulator).
When starting the cold engine, the
control pressure is about 0.5 bar. As the
engine warms up, the warm-up regulator
increases the control pressure to about
3.7 bar (Figure 26).
The control pressure acts through a
damping restriction on the control
plunger and thereby develops the force
which opposes the force of the air in the
air-flow sensor. In doing so, the restriction dampens a possible oscillation of the
sensor plate which could result due to
pulsating air-intake flow.
The control pressure influences the fuel
distribution. If the control pressure is low,

Barrel with metering slits
The slits are shown enlarged (the actual slit is
about 0.2 mm wide).

UMK0044Y

Gasolineinjection
systems

Fig. 15

the air drawn in by the engine can deflect
the sensor plate further. This results in
the control plunger opening the metering
slits further and the engine being allocated more fuel. On the other hand, if the
control pressure is high, the air drawn in
by the engine cannot deflect the sensor
plate so far and, as a result, the engine
receives less fuel. In order to fully seal off
the control-pressure circuit with absolute
certainty when the engine has been
switched off, and at the same time to
maintain the pressure in the fuel circuit,
the return line of the warm-up regulator is
fitted with a check valve. This (push-up)
valve is attached to the primary-pressure
regulator and is held open during operation by the pressure-regulator plunger.
When the engine is switched off and the
plunger of the primary-pressure regulator
returns to its zero position, the check
valve is closed by a spring (Figure 17).
Differential-pressure valves
The differential-pressure valves in the
fuel distributor result in a specific pressure drop at the metering slits.
The air-flow sensor has a linear characteristic. This means that if double the
quantity of air is drawn in, the sensor-


2
1

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6

a In zero (inoperated)
position,
b In operating position.
1 Primary pressure
intake,
2 Return (to fuel tank),
3 Plunger of the
primary-pressure
regulator,
4 Push-up valve,
5 Control-pressure
intake (from warmup regulator).

4

5

Fig. 16

Fig. 17
Primary-pressure
regulator with pushup valve in the
control-pressure
circuit

K-Jetronic

UMK1498Y

1 Control-pressure
effect (hydraulic
force),
2 Damping restriction,
3 Line to warm-up regulator,
4 Decoupling restriction bore,
5 Primary pressure
(delivery pressure),
6 Effect of air pressure.

3

a

b
1

,,,,,
,,,,,
,,,,,
,,,,,
,,,,,

5

2

plate travel is also doubled. If this travel is
to result in a change of delivered fuel in
the same relationship, in this case double
the travel equals double the quantity,
then a constant drop in pressure must
be guaranteed at the metering slits
(Figure 14), regardless of the amount of
fuel flowing through them.

3

4

UMK1499Y

Primary pressure
and control pressure

The differential-pressure valves maintain the differential pressure between the
upper and lower chamber constant regardless of fuel throughflow. The differential pressure is 0.1 bar.
The differential-pressure valves achieve
a high metering accuracy and are of the
flat-seat type. They are fitted in the fuel

21


Gasolineinjection
systems

Differential-pressure valve

a Diaphragm
position with a
low injected
fuel quantity

,,,
,,,
,
,,,,,,,,
,,
,,,,,,,,
,,,,,,,,
,
,,,,,,,,
,,,,,,,,

UMK1656Y

b Diaphragm
position with a
large injected
fuel quantity

,,,
,,,
,,,
,,
,,,,,,,,
,,,,,,,, ,
,,,,,,,,
,
,,,,,,,,
,,,,,,,,

Fig. 18

22

distributor and one such valve is allocated to each metering slit. A diaphragm
separates the upper and lower chambers
of the valve (Figures 18 and 19). The
lower chambers of all the valves are connected with one another by a ring main
and are subjected to the primary pressure (delivery pressure). The valve seat

is located in the upper chamber. Each
upper chamber is connected to a

metering slit and its corresponding connection to the fuel-injection line. The
upper chambers are completely sealed
off from each other. The diaphragms are
spring-loaded and it is this helical spring
that produces the pressure differential.


K-Jetronic

Fuel distributor with differential-pressure valves
2

4

5

6

,,,,
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,,,,,,,,,,,,,,,,,,,,
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8

UMK1602Y

1

3

7

Fig. 19

Fig. 20

If a large basic fuel quantity flows into the
upper chamber through the metering slit,
the diaphragm is bent downwards and
enlarges the valve cross-section at the
outlet leading to the injection valve until
the set differential pressure once again
prevails.
If the fuel quantity drops, the valve crosssection is reduced owing to the equilibrium of forces at the diaphragm until the
differential pressure of 0.1 bar is again
present.
This causes an equilibrium of forces to
prevail at the diaphragm which can be
maintained for every basic fuel quantity
by controlling the valve cross-section.

Mixture formation
The formation of the air-fuel mixture
takes place in the intake ports and
cylinders of the engine.
The continually injected fuel coming from
the injection valves is “stored” in front of
the intake valves. When the intake valve
is opened, the air drawn in by the engine
carries the waiting “cloud” of fuel with it
into the cylinder. An ignitable air-fuel
mixture is formed during the induction
stroke due to the swirl effect.

Mixture formation with air-shrouded fuelinjection valve
1 Fuel-injection valve, 2 Air-supply line,
3 Intake manifold, 4 Throttle valve.

1

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3

4

UMK0068Y

1 Fuel intake
(primary
pressure),
2 Upper chamber of
the differentialpressure valve,
3 Line to the fuelinjection valve
(injection
pressure),
4 Control plunger,
5 Control edge and
metering slit,
6 Valve spring,
7 Valve diaphragm,
8 Lower chamber of
the differentialpressure valve.

Air-shrouded fuel-injection valves favor
mixture formation since they atomize
the fuel very well at the outlet point
(Figures 10, 20).

23